feat!: Update OpenAIEmbeddings' default model to text-embedding-3-small

[davidmigloz]

The new default model of OpenAIEmbeddings wrapper is now text-embedding-3-small.

If you are not planning to migrate to text-embedding-3-small, you have to explicitly set the model to text-embedding-ada-002, otherwise text-embedding-3-small will be used.

final embeddings = OpenAIEmbeddings(
  apiKey: openaiApiKey,
  model: 'text-embedding-ada-002',
);

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https://openai.com/blog/new-embedding-models-and-api-updates#new-embedding-models-with-lower-pricing

text-embedding-3-small is our new highly efficient embedding model and provides a significant upgrade over its predecessor, the text-embedding-ada-002 model released in December 2022.

Stronger performance. Comparing text-embedding-ada-002 to text-embedding-3-small, the average score on a commonly used benchmark for multi-language retrieval (MIRACL) has increased from 31.4% to 44.0%, while the average score on a commonly used benchmark for English tasks (MTEB) has increased from 61.0% to 62.3%.

Reduced price. text-embedding-3-small is also substantially more efficient than our previous generation text-embedding-ada-002 model. Pricing for text-embedding-3-small has therefore been reduced by 5X compared to text-embedding-ada-002, from a price per 1k tokens of $0.0001 to $0.00002.

We are not deprecating text-embedding-ada-002, so while we recommend the newer model, customers are welcome to continue using the previous generation model.